Being left-handed has two main types of effect in cricket: in the pairing of batter vs bowler (and wicket keeper) and in the pairing of two batters. The former is more about placement while the latter is about disruption.
There are relatively few situations in which it’s the fact of being left-handed that brings the inherent benefit. Instead it’s more a case of being a left-handed batter against a right-handed bowler that makes a difference. (The same also applies to being a right-handed batter against a left-handed bowler, just in reverse.) Because being left-handed is much less common, right-handed players will be less familiar with batting or bowling against a left-hander.
Perhaps the biggest advantage is with LBW and the rule about the ball pitching outside the line of leg stump. Being left-handed means this will be the reverse side to usual, so a right-handed bowler may find it much harder to target the stumps while avoiding pitching outside the leg stump line.
Some batters will intentionally bat the “wrong” way, for example a right-handed batter taking the stance of a left-handed batter. This will change which hand is at the top of the handle of the bar. This would normally be done to put more emphasis on control and placement of the ball and less emphasis on the power in the shot.
Bowlers may also be more used to deliveries that swing or spin a particular direction from their perspective, which will have a different effect with a left-handed batter. For example, a ball that swings towards a right-handed batter will swing away from a left-handed batter. This can mean a bowler who uses their “standard delivery” with a particular aim (such as trying to force the batter to edge the ball) may be less successful.
(The counterpart to all of the above situations is that a left-handed bowler will have some benefits. They can counteract the advantages of a left-handed batter on the other team. Their deliveries may also be unfamiliar and disruptive to a right-handed batter. For this reason, some coaches will intentionally try to have at least one left-handed bowler in their squad.)
The right-hand vs -left hand issue can make a minor difference for the wicket keeper when it comes to taking a catch from short distance or collecting the ball for a stumping, depending on whether the ball goes to their left or right. However, a good wicket keeper will have experience dealing with balls on both sides of their body regardless of their handedness.
Being left-handed doesn’t usually make much difference in fielding, though it can make a small difference in some positions. For example, somebody in positions such as backward point and third man might be more likely to need to pick up a ball to their left and then throw it accurately to the wicket keeper’s end for a potential run out. In this scenario, being left-handed could make it easier to pick up and throw the ball without delay, rather than reposition the body or pick the ball up with one hand and throw it with the other.
Beyond the individual match-ups between batter and bowler, being a left-handed batter can also make a difference when playing alongside a right-handed batter. If they rotate the strike frequently, the bowler will need to change their tactics and delivery more frequently, and the fielders will need to change their positions more often. This can disrupt momentum and concentration.
In theory, switching between left-handed and right-handed bowlers can do the same, but batters are used to a change of bowling each over anyway, even if it’s just a change in style rather than left-or-right handedness.