TanteStefana2, it is pretty well explained in many places that isn't true. Any coin that employs mixing wlll have essentially the same bloat (linear factor expansion of transaction count and/or size), except that the base transaction size in Monero is much smaller than in Bitcoin, so even after applying the relevant multiple, the size may still be smaller. DarkSend specifically suffers from the same bloat as Monero, or worse, in terms of using standardized output denomination sizes (some other coinjoin-based systems don't do this and have other problems).
Dash hasfewer/smaller transactions (by smaller I mean making paying fewer payees) on its chain, and many, many fewer using DarkSend (the latter is probably the bigger factor). That is the only reason it's chain is smaller. There is no fundamental technological difference at work.
With Dash it's a choice, that choice has kept our blockchain smaller.
I don't see how a smaller blockchain is any benefit at all if it comes from less use rather than a technological advantage. That would make Truckcoin a great coin.