Scrabble isn't a word game. It's an area-control game with 150,000 rules to define legal placement for your resources. Some of those rules have mnemonics in the form of words you know.
Below a certain level, it is a fun “beer and pretzels” game, where having a good vocabulary helps, and when someone plays an unusual word, the other players “ooh” and”aah.”
Abive a certain level, it is a strategy game requiring a large memorized list of allowable combinations of tiles to play, and the correspondance to actual words has no more significance than the shape of a rook in chess resembling a tower.
The gap between the two games is tremendous, and this is, in my opinion, the game’s only fault. It’s very intimidating to enjoy the beer and pretzels game, but discover that in order to play seriously, it’s not just 10,000 hours of study, but much of that will be rote memorization.
But nevrtheless, the beer and pretzels version of the game is also a valid pursuit. It’s just not the Scrabble you choose to play.
However, if you do not use all of your cards in one turn, you will keep some and can plan ahead a bit, for use later.
Yes, this is an important aspect of area control in Scrabble. Scrabble is about not letting other players play on high-scoring spaces. It's not enough to take them when you can; you have to avoid playing near those tiles so that your opponents won't be able to play on them.