With snap-to on, an instrument you drag snaps into line with the instruments near it, and onto any construction line it comes close to, which keeps rows straight and spacing even. See Construction lines. Click the magnet in the tool row to turn it on or off. A red slash across the magnet means it is off.
Turn it off when you need to place something freely, then turn it back on. While it is off, nothing snaps, instruments you add in the meantime included.