One obvious downside of sticking to Debian’s (snail pace) Tor version: missing security/privacy advantages of later Tor releases.
Do we really want to wait two years to benefit from these kinds of advantages i.e. when a new Debian version is released? This negative will only become larger as the Debian stable version ages.
(my bold)
https://blog.torproject.org/tor-0.4.7.1-alpha-released
This version is the first alpha release of the 0.4.7.x series. One major feature is Vanguards Lite, from proposal 333, to help mitigate guard discovery attacks against onion services. It also includes numerous bugfixes.
&
Major features (Proposal 332, onion services, guard selection algorithm):
Clients and onion services now choose four long-lived “layer 2” guard relays for use as the middle hop in all onion circuits. These relays are kept in place for a randomized duration averaging 1 week. This mitigates guard discovery attacks against clients and short-lived onion services such as OnionShare. Long-lived onion services that need high security should still use the Vanguards addon (GitHub - mikeperry-tor/vanguards: Vanguards help guard you from getting vanned...). Closes ticket 40363; implements proposal 333.