First of all there is quite a bit of confusion about, what a slowroll is, since there are fairly similar poker terms meaning very different things:
Slowroll
A slowroll means putting on an act before calling an opponents all-in with the nuts, when you are closing the action. The Shaun Deep vs. Mike Matusow hand is a good example. Slowrolling dont affect the outcome of the hand but is considered bad etiquette. Personally I am somewhat in between on this, because I find that particular hand hilarious. It was a TV poker show, and Shaun put on some great entertainment for the viewers by doing this slowroll.
In
online poker I never slowroll, because I dont want to run the risk of accidentally timing out and having my hand folded. But if you want to do it, you would need to type something in the chat, because otherwise people dont even know, you are slowrolling them. It might as well be, you were just busy with some other tables, or you had a bad internet connection. So online its a bit of a silly move, which mostly just waste everyones time.
Slowplay
A slowplay means playing a very strong hand in a deceptive way by checking or just calling instead of betting or raising. Depending on the situation this can be a good strategy or a very poor strategy. The best time to slowplay is, when the board is very static, and you wont get drawn out on. Like for instance you have JJ on JJ2. On this board its almost impossible for your opponent to have connected, so its fine to let another card roll off and give them a chance to either catch up or
bluff.
Stalling (playing slowly)
Deliberately slowing down the action is a strategy used in multitable tournaments to increase the chance of making it into the money or getting the next payjump. Its frawned upon by some, and on some sites like ACR they even have rules against it. However on sites, where there are no such rules, like for instance
pokerstars or
888 Poker, its a completely legitimate strategy, and if you never use it, you are leaving some money on the table.