Shin Okada
Explorer
I use minions once per 3 or so of encounters, I guess.
There are powers and abilities which are made to deal with minions. So if a DM don't use minions, players who took such powers will frustrate.
In regard to the effectiveness of minions, it depends largely on terrains and width of the battlefield. Also, there are some non-minion monsters who are tailored for co-working (and even summoning/creating) minions.
Also, encounter's setting and DM's tactics may make minions more important. For example, you can place minions so that PCs (especially controllers) have decide if eliminate as many minions as fast or concentrate fire on stronger monsters.
There are powers and abilities which are made to deal with minions. So if a DM don't use minions, players who took such powers will frustrate.
In regard to the effectiveness of minions, it depends largely on terrains and width of the battlefield. Also, there are some non-minion monsters who are tailored for co-working (and even summoning/creating) minions.
Also, encounter's setting and DM's tactics may make minions more important. For example, you can place minions so that PCs (especially controllers) have decide if eliminate as many minions as fast or concentrate fire on stronger monsters.