any long term financial planning (~10yrs+). e.g. mortgage and retirement planning.
inflation doesn't really matter in short time frames. on any given day, you might get a rent hike, or a raise, or the grocery store might have a sale. inflation is really only relevant over the long term. annual inflation is tiny (2~4%) compared to large unexpected expenses(5-10%). however, over 10 years, even your "large unexpected expenses" will still average out to a small fraction of your spending (5~10%) compared to the impact of compounded inflation (30~40%).
inflation is really critical when you are trying to plan for retirement, which you should start doing when you get your first job. when making long-term projections, you need to consider not only your expected nominal rate of investment return (e.g. 7%) but also subtract the expected rate of inflation (e.g. 3%). alternatively, you can add the inflation rate to your projected spending (being sure to compound year-over-year). when projecting your income 10+ years out, you can use inflation to estimate your annual raises. up to age 30, people tend to get raises that exceed inflation. thereafter, they tend to track inflation.
if you ever decide to buy a house, you need to consider the impact of inflation when calculating the total cost over a 30-yr mortgage. generally, you can expect your house to appreciate over 30 years in line with inflation (possibly more in an urban area). so a simple mortgage projection needs to account for interest, inflation, maintenance, insurance and closing costs.
you could also consider inflation for things like rent and income, but only over several years. generally, rent and income are such large amounts of money it is worth your time to research specific alternatives rather than just guessing what market rates are this year based on average inflation. while it is true that rent and wages go up in line with inflation in the long run, you can make a lot of money in the short run if you keep an eye on market rates every year.
over 10-20 years your personal rate of inflation should be very close to the average rate when you consider all your spending (housing, food, energy, clothing, etc.).