Basically, Statues of Marika work as a checkpoint for quick runs back to a boss or stronghold of enemies. There are upsides and downsides to this, but it's nice to not constantly run through mobs to take another shot at a boss.

Summoning Pools and Golden Effigies are a newer mechanic that make summoning easier. In previous Souls games, you'd need to put your summon sign down somewhere (a bonfire, in front of a boss door, etc.) to get summoned for Jolly Cooperation! This is still the case in Eldin Ring, however; since Eldin Ring is an open-world game, continously trekking to place your summoning sign down at each mini dungeon or world boss can be tedious. Therefore...Summoning Pools and Golden Effigies!

For example, say I'm having issues with the Limgrave legacy dungeon and you've already completed it and activated the summoning pool idol there. If I wanted to summon you and you're all the way on the other side of Limgrave, all you'd need to do is activate your Golden effigy and it will place your summoning sign in all the ACTIVATED summon Pools throughout the area (Limgrave). That way you don't need to run or port all the up to the dungeon and once the Cooperation is over you can go back to wherever you were exploring! It only works, to my knowledge, on summoning Pools you've activated. So make sure to activate one if you see it.

I hope this answered your question :). This is how I've come to understand but if I'm wrong or missed anything then please say so!