Here is when each common line earns its place, and how it settles.
Asian Handicap 0.25
The entry-level quarter line, split between 0.0 (draw no bet) and 0.5. It suits a side you like when a draw is a real possibility. Back the favourite at -0.25 and a win pays in full, a draw returns half your stake and a defeat loses it all. Back the underdog at +0.25 and a win is a full win, a draw is a half win and a defeat loses everything.
Picture Arsenal away at Everton in a tight game you expect them to win. Arsenal -0.5 pays more but loses outright if it ends level; -0.25 pays a little less and hands back half your stake if it does. That is the protection, and a slightly shorter price is what you pay for it.
Asian Handicap 0.75
The workhorse, split between 0.5 and 1.0. Back the favourite at -0.75 and a win by two or more goals pays in full, a one-goal win is a half win, and a draw or defeat loses the lot. Back the underdog at +0.75 and a win or draw pays in full, a one-goal defeat returns half your stake, and losing by two or more loses it all.
Say you think Liverpool will beat Crystal Palace but you're not sure by how many. At -0.5 any win pays in full. At -1.0 a one-goal win is only a refund. The -0.75 sits in the middle, turning that narrow win into a half win, which is exactly why so many bettors reach for it.
Asian Handicap 1.25
Mismatch territory, split between 1.0 and 1.5, such as a Premier League heavyweight against lower-league opposition in a cup tie. Back the favourite at -1.25 and a win by two or more pays in full, while a one-goal win is a half loss: the 1.0 half is refunded and the 1.5 half loses. A draw or defeat loses everything. Back the underdog at +1.25 and a win or draw pays in full, a one-goal defeat is a half win, and losing by two or more loses it all.
A 2-0 or 3-0 wins both halves, so it is the narrow win that stings. If you expect a rout, that risk can be worth the bigger price.
Asian Handicap 1.75 and beyond
Split between 1.5 and 2.0 for -1.75. The favourite needs to win by three or more to collect in full, and a two-goal win is a half win. Anything less loses everything. These are extreme-mismatch lines, and much of the action on them comes in-play, where the numbers are tailored to the state of the game. Treat them as situational tools, not pre-match staples.