I've recently started the piano, and I want to learn all my scales so I know them, but I just can't seem to grasp how these scales actually help when I have a different key signature, sure I know the sharps and flats, bit that doesn't mean I'll recognize them just staring at notes on the page, I don't feel as kf just because I learned thr scale means I'll be able to read In that scale, this is a little demotavting as I really want to learn the piano but I feel like it will take an incredible amount of time to read anything
- Knowing scales eventually does help with sight reading. When fully internalized, knowing instinctively which notes are sharp or flat makes reading easier and helps identify when a piece is changing key. However, this can be a lengthy process and may require great patience.
- Scales also help one encounter different configurations of notes and fingerings that commonly show up in music, even if the literal scale isn't present. Thumb turns, in particular, are an essential piano technique, and scales are an efficient way to practice them. This, too, helps again in sight reading by making it easier to identify particular patterns of notes and the fingerings and/or techniques to execute them.
Each key therefore scale, has its own dedicated set of notes, as you already know.
So, knowing what key a piece is in will help a lot in going 'automatically' to the correct notes on the page. You may see an A note, for example, and knowing the key/scale of the piece is E♭, understand that the A is going to be A♭. Knowing the key/scale is actually B, then that A note will become A♯. It also works in other keys - knowing the key/scale is D, then that same written A will automatically be, in that piece, A♮!
Before sight-reading a new piece, my students need to play the scale it's in. That puts them 'in the zone', and means they're more likely to play diatonic notes correctly. It also highlights the accidentals, which are all the altered notes that don't usually belong in that key.
I disagree somewhat with Aaron's last reason, though, as it's rare that there is more than a snippet of a scale run in a piece, so knowing the fingering for a particular scale, and trying to apply it for a short run, may well need the 'wrong' fingers for those notes in that piece.. However, scales do need thumb action to be fluid, so learning how to get that will be facilitated by learning it in scales.