Gin is very often served with a tonic or flavour mixer and is rarely thought to be drunk straight unlike whiskey, rum, or tequila.
A pure juniper-forward taste profile is regarded as a harsh and pungent mix of fresh woody pine and not the most pleasant experience without accompaniment.
A sipping gin is an exception and is already balanced with a mix of botanicals to reduce the impact of the juniper and be sipped without the need for a tonic or a mixer. Though that is a choice and they can still be pleasantly mixed with the addition of a tonic.