How do you decide when to multi class?

[MarkVIIIMarc]

In the big sense here.

My only 5e example is my level 5 Lore Bard. I sure am going to take level 6 for magical secrets. Then I'm thinking about dipping in Wizard or maybe Rogue.

Wizard would fit in with some role playing we did. Rogue would be an odd ball but give mad skills.

I am thinking my table is a bunch of wargamers and the DM and us are pretty straight forward with damage. Some of my more creative spells (Phantasmal Force) don't seem as well taken as Thunderwave.

So the Warlock would give the EB spam and some ability to get a bit more interesting with my CN character.

What makes you all decide to go multi?

[bluthunda]

When I'm making a character if im thinking about multiclassing I typically consider my overall character concept before mechanics but if the classes are basically the same concept wise like Fighter Barbarian which go together easily and basically doesn't effect overall concept.
My most recent character was a Paladin/Warlock in which his pally diety and great old one patron were the same so I think it worked well. In this case I was mostly going for the Smite ability and some spell slots from pally so I started going Warlock after lvl 2. But usually you wanna get those ASI before multiclassing out .

[RakiReborn]

A character I play in a longer running campaign started as a sorclock. At level 9 (sorc6/lock3), it became clear that in the party we desperately needed some more utility spells, so I decided to multiclass wizard (had great rolled stats so that was no problem) for the wide spell list. The char is currently lock3/sorc6/wiz2, and I will probably continue in sorc for a while again, but might go on in Wiz a bit depending on the needs of the party.
My main concept for multiclassed characters is usually already written in its background, and planned with creation, but sometimes I am willing to adjust for the needs of the party and what happens in the story.

[Spacehamster]

I always want to multi class, old damage to my way of thinking from 3.5e. :p

[Aaron Underhand]

Role play should decide mostly, but I like to multiclass early to get the character flavour established, unless it's some later event that triggers the change.

My (point buy) vHuman Lore Bard always wanted to be a wizard, but upbringing and talents lead to him being Bard first - I took wizard at second level, realized I wasn't a very good wizard, and have been Bard ever since.

Delaying Bard features is painful, but the utility of wizard spells at first level, and first level rituals, has given me much more freedom in selecting Bard spells to compliment the party (no other arcane caster). Still it's a long haul to Bard 6 while being one level behind, and your ASIs are delayed as well.

The beauty of the wizard dip is you still get full spell slots. Coupled with your increased choice a one level dip means you feel "behind" only on odd levels, and only for your highest level spells. Rogue would put you one level behind all the time (and give you much more constrained spell selection), plus you're jack of all trades - rogue 1 dip gives you less extra to skills than it would for other characters.

Warlock 2 dip is undoubtedly powerful in the at-will damage stakes, though you're unlikely to use Hex give the other demands on your concentration, and it will slow both casting progression and spell slots. Your call, but if you have the stats for it I recommend wizard for the diversity, flexibility and fun.

Of course if you can get cleric there are options with knowledge cleric or arcana cleric and both also give you a great AC boost (medium armour and shield)

Note a three level dip means you miss the 9th level magical secrets (wish)... may be a consideration.

[Specter]

I think the main concerns are ASI's and being functional.

In your case, if you don't have a maxed Charisma it's never a bad idea to wait for level 8 and do it.

About being functional, at level 6 you are already a full-functioning Bard with short-rest inspiration and any spells you may want to fill holes. Rogue 2 for Cunning Action would be a good call.