Well, if we take the major key sigs: There is C major without sharps and flats, then there are 7 major sigs from one sharp to seven sharps and finally 7 major sigs from 1 flat to seven flats. Total is 15.
Similar there are 15 minor key sigs. So the total is 30.
That is what I have learned, so nothing new in that.
Since you can actually encounter all of them in sheet music you are better off knowing them all. As an example you need to be able to read a key sig with 6 sharps as well as a key sig with 6 flats even you can argue it is the same thing on a piano. If you can only read one of them you will be in trouble when you encounter sheet music with the other one.
On different instruments the notation can make a big difference. Like on a violin a B♭ is intonated in relation to A♮ like a leading note down to A;
while the note A♯ will be intonated in relation to B♮ like a leading note up to B.
The point is that A♯ and B♭ will be two different pitches, thus the notation makes a big difference.
You won't always intonate like that, it depends on the context. It is called expressive intonation.
Other times you will play with just intonation, typically with double stops.
If you play in an ensemble the intonation is related to the ensemble.
If you play with a piano the unison sections will be intonated with equal temperament since you want the unison to actually be unison.
Anyway the notation can make a big difference on how you play.
Note that on a concert harp (pedal harp) it makes sense to have up to seven sharps or seven flats. The harp is tuned in C♭ major (each octave has 7 strings), then with the 7 pedals you can raise the strings a half step up to C major and another half step up to C♯ major. Thus when accidentals occur they can show on which string you are playing. You can play a B both with the B♭ string changed to B♮ with the pedal, or with the C♭ string in default position. The notation can show which string to use.
Thus it can make sense to notate a B major scale as a C♭ major scale; well, you can also, with the pedals, change all the strings into a B major scale and thereby use a B major motation. Note that a B and a C♭are two different strings, the B is the B♭ string raised a half step with the pedal while the C♭ is the C♭ string.
Anyway, I might have gotten carried away, my overall point is that it is a good idea to know all the key sigs from no signs up to either seven sharps or seven flats.