It's the swimming that many tourists come for and it truly is a great place for a dip, much like Kuang Si.
It's difficult to suggest one over the other as they each have their charms, but you will see a greater proportion of tourists at Kuang Si than Tad Sae.
Often at the entrance there are a group of elephants you can ride and feed, convenient if you can't be bothered going on a formal tour to one of the nearby elephant camps.
During the height of the dry season the falls are hardly a trickle, so you're better off going to Kuang Si then. The site is more popular with locals than tourists, so dress modestly to avoid causing offence. There are full facilities including public toilets, changing rooms and simple restaurants.
How to get there
A tuk tuk can only take you as far as the banks of the river and then a boat serves as transport across to the falls (10,000 kip). Kuang Si has overtaken Tae Sae in popularity, but during the wet season tour operators streamline the process of getting there and offer shared transport at better rates than you can negotiate for yourself unless you're travelling with a sizeable party.
During the wet season, you can reserve a seat in a minivan or tuk tuk for around 50,000 kip. Chartering a tuk tuk for the return trip to the falls (including waiting time) should cost around 150,000 kip.