Bond funds mainly invest in bonds. You may ask, just buy bonds yourself. Why do you invest indirectly through bond funds? Perhaps, the expected return of bond funds is lower than that of equity funds, so why invest in bond funds?
First, investing in bond funds can buy more "good" bonds. You may be familiar with treasury bonds investment. Just go to the bank counter and buy it (voucher-type government bonds). In fact, there are fewer types of bonds that individuals can invest in than bond funds. Individuals can only buy voucher-type treasury bonds, book-entry treasury bonds, voucher-type or book-entry corporate bonds (there are few voucher-type corporate bonds issued to ordinary investors at present) and convertible corporate bonds, and cannot buy or sell treasury bonds and financial bonds traded in the interbank market. If you invest in bond funds, you may "buy" many corporate bonds with higher interest rates, or you may "enter" the inter-bank bond market to buy and sell financial bonds and government bonds traded there to obtain higher returns.
Secondly, by investing in different kinds of bonds with different maturity structures, more potential benefits can be created than a single bond. The main risk of bonds and bond funds is interest rate risk, while bonds with different maturities have different sensitivity to interest rates, and the price of long-term bonds is greatly affected by interest rate changes. If the interest rate rises, the price of long-term bonds will fall, which will cause losses to bondholders.
Thirdly, investing in bond funds has better liquidity than investing in a single bond. Generally speaking, bonds are repaid at maturity. If you invest in treasury bonds traded over the counter of banks, once you need money, the handling fee for selling bonds is relatively high. By indirectly investing in bonds through bond funds, you can get higher liquidity and redeem your own bond funds at any time, with relatively low cost.