I think you are confusing "slowrolling" with playing a hand "slow" or "Hollywooding."
Playing a hand "slow" is to have a good hand like AA and check or call passively to induce the opponent(s) into action for you and then you can trap them later in the hand. Playing "fast" by value betting, raising and re-raising is generally more profitable, but playing "slow" is a viable strategy.
Hollywooding is a slang term for a poker player "acting" and giving the impression that their decision is tougher than it is, or that their hand is different from what they are trying to convey. This would include something like taking a long time to "think" about calling on the River when you hold an Ace-high Flush (nuts likely the best hand) but there are players after you left to act. This is justifiable by strategy because you are hoping to get the players left to act after you to put in their chips (when they would have a quick fold if they believed your hand was strong).
Slowrolling is, however, poor sportsmanship and different from the above two cases though. Slowrolling is like Hollywooding, but wasting the time when there is no strategy reason to do so. Basically, they are being a jerk by intentionally stalling the game just to crush your hopes when they finally reveal their better hand after a long wait.
The classic slowroll move is on the River when they are LAST to act with a hand which is a snap-call. Say one opponent is All-In, but the Slowroller is on the Button (last to act) and has the best possible hand on the River (something like Four of a Kind in Aces when no Straight Flush is possible). The slowroller wouldn't snap call like most would, but rather take forever to "decide" and then call after a long wait. Unlike the example above where others left to act might invest chips, the slowroller is last to act and just wastes everyone's time.
Slowrolling is arguably the most disrespectful move a poker player could make and usually players at a table would rally against a slowroller if it occurred in a game.
Here is a comical representation to illustrate what slowrolling is and how people generally react:
https://www.youtube.com/watch?v=HOPOhIxeIZE