DS will be 3 in two months, and we just do everything together. He cannot/will not play by himself for any period of time, ever. He's very sociable and extroverted and needs lots and lots and LOTS of interaction; much more than I could supply by myself even if I could give him 100% of my attention all the time.
If we go about doing a task together, then yes, it takes longer than if he weren't around, but it gives him some of that interaction that he needs and he loves to contribute and feel helpful. There is almost always something I can give him to do - match socks or fold rags, break the yolks in the bowl when we make breakfast, stir something, he can put his own clothes away and put the silverware away, he can help sweep (with his own little broom), he can drag the recycling bin outside, he can use his little spray bottle of water and a rag when we're cleaning bathrooms, he can sit on the counter and help me rinse dishes. Having him always by my side does afford me a little bit of leeway when I do need to do something without him. We'll have a mini-play session where I chase him or get him giggling somehow, then when he's cup is super full I can say, "I'm going to make a phone call. Why don't you play with blocks until I'm finished." Giving him something to do while he waits for me to be finished is key. Even better if it's a task I ask him to complete. In my less inspired moments I just ask him to count and see how long it takes me to finish whatever I need to do.