Due to their bright colors, mines can be pretty easy to spot in wide open spaces. However, if it's used in narrower spaces, it can be a very effective tool to, for example, block paths your enemies can use to flank your team or even to cover a friendly's escape with the flag without actually needing to stay behind.
If you're concerned about friendly fire... ahem, I mean explosions, well, you can rest easy knowing that your mine won't accidentally blow up a teammate. Mines can only be activated by players from the opposing team, and in the case of deathmatches, your mine can be activated by any enemy player.
Although mines are incredibly useful, it does have some disadvantages. For instance, the mine will disappear if the owner of the mine is destroyed and staying alive can be quite difficult without sufficient support from other team members. Mines will also disappear when a match is over.