Mod can be installed on server what gives better functionality.
Mod functionals being installed on Server or on Client, and gives Best Experience if installed on both sides.

Player with mod installed on client can join servers without mod and use it as client-side only,
it works well, but gives a few little bugs.

Known bugs:

• The side of placed side-related block wont depend on side of other block where player is placing it, but on player's facing in the world (link)

Player without mod can join server with mod and use its functional through command:

/buildingshift (toggle|on|off) <player target (only for ops)>

In this case player will experience a few other bugs related to missing client-side code.

Known bugs:

• No sound after placing the block
• Unabbility to spam blocks row

And, the Best Experience, is when Player with mod installed on client plays on Server with mod installed too. It makes Player and Server side of mod communicate better:

• Player will see indicator beside crosshair
• Player wont experience bug related to mod being installed either only on server or only on client

Playing in singleplayer is the same as playing with mod installed on both sides, but on integrated server.