Careful Spell and Evard's Black Tentacles?

[MaxWilson]

in any case, basically it's supposed to work well with fear, confusion, and hypnotic pattern, be frankly pretty bad with AoE damage spells but at least not completely non-functional, and to not work well at all with basically anything else. if you really love one of those three spells but have to constantly worry about friendly fire, or if you have a full party of people with evasion and love fireball, consider learning careful spell. otherwise, you can leave it alone until later. or never.

Or just see if your DM is willing to go by the actual PHB text instead of Twitter, and enjoy the awesomeness that is Careful Evard's Black Tentacles. And yes, always passing your saves means you will neither be restrained nor take damage, although you do have to deal with the difficult terrain.

As far as PHB wording is concerned, Heighten Spell is restricted to affecting the "first saving throw" whereas Careful Spell is not. Reasonable inference: it works every time a protected creature (which you selected when cast the spell and used Careful) is asked to make a saving throw against (that particular casting of) the spell.