Assuming you're able to keep the water free from contaminants, then there is no reason not to do this as long as you're doing partial boils. It's simple, effective and avoids the need for additional equipment.

A chiller becomes more of a necessity as you step up to whole wort boils. One cited advantage of chilling the entire wort with a immersion chiller is that it keeps the cold break out of the fermentor, leading to a cleaner more stable beer, although how much of an advantage this is is still debated.

Assuming you're able to keep the water free from contaminants, then there is no reason not to do this as long as you're doing partial boils. It's simple, effective and avoids the need for additional equipment.

A chiller becomes more of a necessity as you step up to full wort boils. One cited advantage of chilling the entire wort with a immersion chiller is that it keeps the cold break out of the fermentor, leading to a cleaner more stable beer, although how much of an advantage this is is still debated.